Note: Descriptions are shown in the official language in which they were submitted.
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Infection Mold Assembly For Molding Plastic Containers
The present invention relates generally to manufacture of plastic
containers for containing paint or other materials, and more particularly to a
new
apparatus and method for injection molding plastic containers that are adapted
to be sealed off by removable lids.
Field Of The Invention
As is well known, the ordinary one-gallon paint can has been made of
steel and is provided with a friction fit lid that also is made of steel. In
the paint
industry prevention of leakage is important since paint cans frequently
encounter
rough handling while being transported or stacked for storage or retail
display.
Consequently a substantially hermetic seat is required between the paint can
and its lid. This is achieved by a friction fit air-tight engagement between
the lid
and container which is such as to permit the lid to be removed manually using
a
suitable prying tool. In addition, the standard metal paint can lid does not
protrude beyond the perimeter of the paint can so that as. to prevent
accidental
disengagement of the fid. The configuration of the interlocking connection
between the standard metal paint cans and their metal lids is such that the
lids
remain tightly in place even when subjected to the action of paint shaking
machines or to other severe handling or shock conditions. Further the lids can
be re-attached to again provide a fluid tight seal with the .container.
However
standard metal paint cans have certain shortcomings, one of which is the
tendency to corrode.
In the past, efforts have, been made to provide containers for paint that
are made of plastic. For example, U.S. Patent No. 5,097"977, issued March 24,
1992 to R. Straub illustrates a closure assembly for a container that
comprises a
snap ring connected to the top of the container and a lid that is removably
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attached to the ring so as to close off the container. A similar arrangement
is
disclosed by U.S. Patent No. 4,619, 373, issued Oct. 28, 1986 to H.W. Galer.
Other plastic paint can designs andlor apparatus for injection molding same
are
illustrated by the following U.S. Patents: 4,777,004, issued Oct. 11, 1988 to
H.W. Galer; 4,619,373, issued Oct. 28. 1986 to H.W. Galer; 4,349,119 issued
Sept. 14, 1982 to I. Letica; 4,512, 494, issued April 23, 1985 to J.W. Von
Holdt;
4,383,519 issued May 17, 1983 to 1. Letica; 4,293,080, issued Oct. 6, 1981 to
1.
l_etica; and 3,977,563 issued Aug. 31, 1976 to W. G. Holt.
However, prior plastic paint canllid designs have suffered from various
limitations, such as need for complex and costly injection molds, not capable
of
being handled by standard filling, labeling and packaging machinery,
inadequate
strength, unretiable sealing of lid to container, andlor lack of appeal to
prospective customers.
A new plastic containerlremovable lid construction is disclosed
and claimed in U.S. Patent No. 6,250,494, filed March 30, 1999. The plastic
container construction disclosed in my copending application offers numerous
advantages. It has a one-piece construction free of any seams or crimps, does
not
rust internally and requires no internal protective coating, has a higher
dynamic
compression that metal paint cans, can be manufactured in different colors and
surface finishes, weighs less than a metal can of comparable size and volume,
can
be molded with embossed printing so as to eliminate the need for a subsequent
labeling operation, and is adapted to be closed off by a complementary lid
that
makes an air-tight seal and can be removed and replaced without damage. The
container rim and a complementary lid are adapted to interlock in a manner
which
provides an air-tight friction fit, permits the lid to be easily removed by
use of a
prying tool, and assures that the lid cannot be accidentally dislodged as a
consequence of being subjected to impact, shock or stress in the course of
being
stacked or transported.
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Summary Of The Invention
The primary object or purpose of the invention is to provide a new and
improved injection molding apparatus for use in manufacturing plastic
containers
that embody the construction disclosed and claimed in said U.S. Patent No.
6,250,494.
A more specific object is to provide an injection mold apparatus for
manufacturing one-piece plastic containers having lid-receiving rims that
project
inwardly of the side walls of the containers.
Another specific object is to provide an injection mold assembly for
molding plastic containers that does not require a collapsible core.
A further object is to provide an improved method of injection molding an
improved plastic container for use in storing paint or other material.
A further is to provide a novel method and apparatus for manufacturing a
plastic container that is adapted to releasably interlock with a lid in a
manner that
provides positive line contact sealing of the container.
Another object is to provide a novel method and apparatus for injection
molding a one-piece, substantially straight-sided plastic container for paint
or
other liquid or particulate material that is characterized by a rim-to-lid
interlock
which provides an air-tight friction fit, permits the lid to be easily removed
by use
of a prying tool, and assures that the lid cannot be accidentally dislodged as
a
consequence of being subjected to impact, shock or stress due to rough
handling in the course of being stacked or transported.
Still other objects and features of the invention are disclosed or rendered
obvious by the following detailed description which is to be considered
together
with the accompanying drawings.
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Brief Description Of The Drawings
Fig. 1 is an exploded sectional view in elevation showing a container and
a lid therefor that embody the invention disclosed in said U.S. Patent No.
6,250,494.
Fig. 2 is an enlarged scale fragmentary sectional view in elevation
showing details of the rim on the upper end of the same container;
Fig. 3 is a sectional view taken along line 3-3 of Fig. 2;
Fig. 4 is an enlarged fragmentary sectional view in elevation of the lid;
Fig. 5 is a fragmentary sectional view on an enlarged scale showing how
the lid interlocks with the rim of the container;
Fig. 6A is a schematic sectional view in front elevation of a mold assembly
embodying the present invention in fully closed position;
Fig. 6B is a schematic sectional view is side elevation of the same mold
assembly in closed position;
Figs. 7A to 10A are additional sectional views in front elevation that
illustrate how the mold is operated;
Figs. 7B to 10B are schematic sectional views in side elevation that
illustrate different mold positions correspond to the positions shown in Figs.
7A to
10A respectively;
Fig. 11 is a fragmentary sectional view on an enlarged scale showing the
core plate latching mechanism with the mold assembly in the fully closed
position;
Fig. 12 is a fragmentary sectional view on an enlarged scale of the
components of the mold assembly for molding the rim section and one of the ear
sections of the container shown in Figs. 1-3;
Fig. 13 is a fragmentary sectional view similar to Fig. 12 taken at a
position that is located approximately 90° away from the viewpoint of
Fig. 11;
Fig. 14 is a fragmentary sectional view taken along line 14-14 of Fig. 12;
and
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Fig. 15 is an enlargement of a portion of Fig. 13.
Description Of Container And Lid
Fig. 1 illustrates an injection-molded substantially straight-sided container
2 and a lid 60 that embody the invention disclosed and claimed in said
U.S. Patent No. 6,250,494.
Container 2 is made of a suitable plastic material that provides an
adequate combination of resiliency and strength, e.g., high density
polyethylene.
Container 2 comprises a side wall 4, and a bottom wall 6 which preferably is
contoured as shown to provide a flat annular downwardly projecting rib 8 for
strengthening purposes. Side wal! 4 is a substantially constant diameter
cylinder. However, if desired, side wall 4 may be tapered so that the upper
end
has a slightly larger diameter than its bottom end. The bottom end of the
paint
can also has an axially extending seating flange 10 that forms a continuation
of
side wall 4. The side waif also has two diametrically opposed perforated ears
12.
As seen in Figs. 2 and 3, ears 12 comprise a curved side wall 14 that extends
through an angle of at least 180° degrees, preferably about
200°, and a front wall
16 that has a tapered hole 18 for acceptance of one end of a wire handle (not
shown) of the kind commonly used on metal paint cans. Hole 18 serves as a
pivot point for the wire handle.
Referring specifically to Fig. 2, the upper end of the side wall 4 is formed
with a split or bifurcated rim, the rim comprising an outer rim section 20, an
inner
rim section 22, and a rim-connecting section 24. The outer rim section 20 is
essentially an extension of side wall 4 and has an outer surface 26 that
preferably, but not necessarily, projects radially slightly beyond the outer
surface
28 of side wall 4. Surface 26 may be a straight cylinder or, as shown, may
extend at a slight angle to outer surface 28. Preferably, but not necessarily,
the
upper end edge of outer rim section 20 is rounded off as shown at 30. The
inner
surface of outer rim section 20 is identified generally by numeral 32. Inner
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surface 32 extends at a selected acute angle, e.g., an angle between 6 and
7°,
to side wall 4 and the longitudinal center axis of the container. Preferably,
but
not necessarily, the diameter of the upper end of inner surface 32 is enlarged
so
as to provide an offset or recessed cylindrical surface portion 34 that
extends
substantially parallel to the longitudinal (vertical) axis of container 2. The
inner
surface 32 also is formed with two locking or gripping ribs 36 that are convex
in
cross-section and preferably extend around the full circumference of the
container rim. Alternatively, the ribs 36 could be interrupted at selected
points
about the circumference of outer rim section 20.
The inner rim section 22 is located inwardly of side wall 4. Rim section 22
has substantially parallel outer and inner surfaces 40 and 42, with at least
surface 40, but preferably also surface 42, extending at a selected acute
angle,
e.g., an angle between about 9° and 10°, to the side wall 4.
Preferably, but not
necessarily, surface 40 of rim section 22 is smooth. However, it could also be
provided with gripping ribs similar to ribs 36. Preferably, but not
necessarily, the
upper end edge of rim section 22 is rounded as shown at 44.
Preferably but not necessarily, the rim-connecting section 24 is formed
with a generally concave upper surface 46. The bottom surface 48 of section 24
preferably forms a gentle curved transition between the inner surface 42 of
inner
rim section 22 and the inner surface 50 of side wall 4.
Surfaces 32, 40 and 46 together define an annular locking channel for a
lid 60 hereinafter described. In this connection, it should be noted that the
surface 40 of inner rim section 22 is not parallel to the inner surface 32 of
outer
rim section 20; instead those surfaces are in a converging relation with one
another away from rim-connecting section 24. Preferably they converge on one
another at an angle of between about 2° and 4° with increasing
distance from
bottom wall 6. In other words, the spacing between surfaces 32 and 40 is
greatest near surface 46 and smallest near the top end of rim section 22.
The outer rim section 20 is provided with one or more notches 58 at its
upper edge (Figs. 1 and 2) to facilitate removal of a plastic lid or cover 60.
Lid 60
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preferably is made of the same material as container 2. The lid is circular
and
comprises a generally flat center or crown section 62 that preferably, but not
necessarily, is dimpled at its center as shown at 64, and a convoluted rim
section
identified generally by the numeral 66 that is adapted to mate with the
bifurcated
rim section of container 2.
As seen best in Fig. 4, the convoluted rim section 66 of the lid or cover is
characterized by a first upstanding circumferentially-extending rib that
comprises
an inner wall or leg section 68 that is joined to an outer wall or leg section
70 by
a curved connecting wall section 72. The inner section 68 has an outer
peripheral surface 74 that is substantially cylindrical and parallel to the
center
axis of the lid, while the outer section 70 has an inner circumferentially-
extending
surface 76 that is canted with the respect to the wall surface 74. Surface 76
is
slanted extending downwardly and inwardly at an angle to the center axis of
the
lid that is approximately the same as the angle of the surfaces 32 and 40
relative
to the center axis of the containers. Preferably, surface 76 extends at an
angle
of about 7° to 10° to the center axis of the lid.
The wall section 70 also forms part of a second downwardly projecting rib
that also comprises an outer wall section 80 and a curved connecting wall
section 82. Outer wall section 80 also has an outer surface 84 that extends at
an angle that preferably is substantially the same as the angle of the surface
76.
Alternatively, wall section 80 may be formed so that the angle of outer
surface 84
relative to the lid's center axis is slightly greater than the angle of
surface 76,
e.g., 1°-3° greater. The upper end of wall section 80 has an
outer peripheral
surface portion 86 that is essentially cylindrical and is parallel to the
center axis
of the lid. Surface portion 86 projects outwardly beyond surface 84, so as to
form a shallow shoulder or ledge 88. Additionally the outer surface 84 is
provided with a pair of locking or gripping ribs 90 that preferably are convex
in
cross-section as seen in Fig. 4. Ribs 90 are designed to mate and interlock
with
the similarly shaped ribs 36 formed on the container rim. Ribs 90 preferably
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extend around the full circumference of surtace 84, but alternatively they
could
be interrupted at selected points about the circumference of surface 84.
Making the container and lid of a resilient strong material such as a high
density polyethylene is advantageous, particularly in the case of making one
gallon paint cans, in that the material provides the container with sufficient
strength to resist deformation under the weight of one or more like-filled
containers. At the same time, the plastic material can flex sufficiently to
allow the
lid to be secured in place on the container so as to seal off the container's
contents.
The downwardly projecting rib on the lid formed by wall sections 70, 80
and 82 is designed to make a friction fit in the channel formed between the
outer
and inner rim sections 20 and 22 of the container. The distance between the
surfaces 76 and 84 of the downwardly projecting rib of the rim may be equal to
but preferably is slightly in excess of the distance between the surfaces 32
and
40 of container rim sections 20 and 22 respectively. However, that rib is
sufficiently resilient as to allow sections 70 and 80 to be forced toward one
another under a radial compressing force. Consequently, as shown in Fig. 5,
when the lid is attached to the rim section of the container, the depending
rib
comprising wall sections 70, 80 and 82 makes a tight friction fit in the
channel
between rim sections 20 and 22, with the gripping ribs 90 interlocking with
gripping ribs 36.
When the lid is attached to the container, its periphery is surrounded and
protected by the upper end of rim section 20. The maximum outside diameter of
the combined container and lid is essentially the outside diameter of the
outer
rim section 20 measured at the upper edge of its outer surface 26. Since that
diametrical dimension is nearly the same as that of the outer diameter of wall
4,
the container with the lid attached has an appearance substantially the same
as
a sealed conventional metal paint can. Removal of the lid from the can is
facilitated by the presence of notches 58 in the upper end of rim section 20.
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Notches 58 permit a screwdriver or other tool to be engaged with shoulder 88
to
pry the lid off of the container.
Description Of The Preferred Embodiment
A preferred embodiment of the mold assembly of the present invention is
a mold assembly as shown in the drawings that is designed to produce a one
gallon container having the construction shown in Figs. 1-3.
Referring now to Figs. 6A and 6B, there is shown a mold assembly that
comprises a first or front plate 102, a second or back plate 104, an ejector
plate
106, a core support plate 108, and a support plate 110. Use of the terms
"front"
and "back" is premised on the fact that in conventional injection molding
machines the molds are generally oriented horizontally, i.e., rotated
90° from the
position shown in the drawings, and they open and close by relative movement
along a horizontal axis. However, the mold assembly is illustrated with a
vertical
orientation in the drawings for the purpose of making it easier to understand
its
construction and mode of operation.
The front plate 102 is adapted to be securely mounted by threaded bolts
103 to a stationary platen (not shown) of an injection molding machine (also
not
shown), while back plate 104 is adapted to be mounted by additional threaded
bolts 105 to a movable platen (not shown) of the same injection molding
machine. Front plate 102 has a sprue hole that is fitted with a hollow sprue
bushing 107 for connection to a source of plastic material to be injected into
the
mold assembly. A plurality of leader pins or guides 112 (only one of which is
shown in Fig. 6A) are fixed to and extend between back plate 104 and support
plate 110. A second plurality of leader pins or guides 113 (only one of which
is
shown in Fig. 6A) are fixed to support plate 110 and mounted in telescoping
relation to guide bushings 115 attached to front plate 102. A support pillar
in the
form of a solid cylindrical rod 114 is fixed to back plate 104 and extends
toward
the support plate 110. Ejector plate 106 and core plate 108 have slide holes
117, 119 through which leader pins 112 extend, with the slide holes being
sized
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so that leader pins 112 prevent lateral movement of the ejector and core
plates
while allowing them to move lengthwise of the leader pins toward and away from
support plate 110. Ejector plate 106 also has a slide hole 121 through which
extends support pillar 114. Pillar 114 terminates a predetermined distance
from
back plate 104, and functions as a rear stop member for core plate 108. A
second support pillar in the form of a solid cylindrical rod 116 is attached
to and
partially overlaps the adjacent end of support pillar 114. Support pillar 116
extends through a slide hole 123 in core plate 108 and engages support plate
110. Support pillars 114 and 116 together prevent support plate 110 from
collapsing away from front plate 102 under molding pressure when the mold
assembly is closed and injected with plastic as described hereinafter. Four
pressure pins 139 (only one of which is shown} are slidably mounted in
bushings
141 affixed to front plate 102. Pins 139 and bushings 141 are distributed in a
rectangular pattern around cavity member 174 (described hereinafter). A coil
compression spring 143 in bushing 141 urges pin 139 toward core support plate
108. The purpose of pin 139 is to urge plate 108 back away from plate 110 as
the mold assembly moves from the fully closed position of Figs. 6A, 6B to the
open position shown in Figs. 9A, 9B and 10A, 10B.
The ejector plate 106 is adapted to be connected by a threaded member
125 to an operating member of the injection molding machine (not shown) which
moves it toward and away from the front plate 2 during the injection molding
cycle described hereinafter. Member 125 extends through a hole 127 in back
plate 104 that is sized to allow reciprocal axial motion of member 125. Fixed
to
ejector plate 106 is a poppet 118 having an enlarged head 120 at its front
end.
Poppet 118 extends slidably through a hole in core plate 108.
A cam bar 122 is attached to the periphery of support plate 110. Cam bar
122 projects rearwardly from support plate 110 toward back plate 104. Attached
to ejector plate 106 in line with cam bar 122 is a latch bar 124. Bar 124 is
slotted
longitudinally as indicated at 126 to slidingly receive cam bar 122. The open
side of slot 126 faces core plate 108. Referring now to Figs. 6 and 11, the
inner
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edge of latch bar 124 is notched as shown at 128, and the forward end of the
latch bar preferably has a projection 130 that extends into a notch 132 in the
periphery of core plate 108. The notch 128 serves to receive a flat detent pin
132 that is mounted in a radially-extending hole 134 in core plate 108. A
threaded lock pin 136 screwed into a tapped hole in core plate 108 extends
through an elongate hole 137 in detent pin 132 to limit axial movement of the
detent pin in hole 134. A compression spring 138 in hole 134 urges detent pin
132 into notch 128. The back edge of notch 128 forms a flat shoulder 140 which
is intercepted by the detent pin 132 when the pin is in its extended position
(Fig.
11 ). Consequently when ejector plate 106 is moved forward toward front plate
2,
the movable latch bar 124 acts through detent pin 132 to releasably lock core
plate 108 to ejector plate 106, thereby causing the core plate to move forward
with the ejector plate.
However, cam bar 122 has an inclined inner edge cam surface 142 at its
back end. Surface 142 is positioned to engage detent pin 132 when core plate
108 moves with ejector plate 106 towards support plate 110. As ejector plate
106 and core plate 108 move toward support plate 110, the slanted edge cam
surface 142 of cam member 122 engages detent pin 132 and cams the detent
pin into cavity 134 out of engagement with shoulder 140, thereby freeing
movable latch bar 124 (and hence ejector plate 106) from its locked connection
to core plate 108. Cam bar 122 and movable latch bar 124 are sized and
disposed so that the cam surface 142 engages and pushes the detent pin back
into the cavity 134 just as the core plate 108 engages the stationary support
plate 110, thus freeing the ejector plate from the core plate so as to allow
the
ejector plate to continue moving toward the front plate, carrying with it the
poppet
118. During further movement of ejector plate 106 toward front plate 102, the
inner edge 144 of latch bar 124 holds the detent pin in its retracted
position.
Support plate 110 has a center hole in which is fixed a ring member 146.
The latter in turn surrounds a core member 148 which is fixed to core plate
108.
Core member 148 has a center hole 150 which slidably receives poppet 118.
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The upper end of hole 150 is tapered outwardly, i.e., flared, as shown at 152
(Fig. 7A) so as to nestingly receive the enlarged head 120 of poppet 118.
Turning now to Figs. 12 and 13, ring member 146 is formed at its front
end with a forwardly projecting annular rib 154. Rib 154 is sized and
contoured
so as to conform to and mold the surfaces 32, 40 and 46 and a part of the
surface 26 of rim sections 20, 22 and 24 of the container shown in Figs. 1-3.
In
this connection, it should be noted that Figs. 12 and 13 illustrate at 160 the
injected plastic material that forms the container. Rib 154 has a pair of
grooves
155 (Fig. 13) on its inner surface which are shaped to form the locking
projections 36 shown in Figs. 2 and 5. The inner side of ring member 146 is
provided with a tapered surface portion 162 which is joined to a cylindrical
surface section 163. As shown in Fig. 12, the inner diameter of ring member
164
is smallest at cylindrical surface section 163.
Referring now to Figs. 6A-10B, 12 and 13, the core 148 is formed with a
generally cylindrical outer surface 164 which is joined to a reduced diameter
tapered surface 166. The latter surface joins a surface 168 which is shaped to
form the inner surface of rim section 22 of the container. Rearwardly of
surface
168 the core 148 has surfaces 170 and 172 which are contoured so as to mate
with the surfaces 162 and 164 respectively of ring 146.
Referring again to Figs. 6A-10B, 12 and 13 a cavity member 174 is
secured to front plate 102. The latter has a cavity defined by a cylindrical
side
surface 176 and an end surface 178 which are shaped to conform to and mold
the outer surfaces of side wall 4 and end wail 6 respectively of the container
shown in Figs. 1-3. The inner end surface of bushing 107 is shaped to conform
to and mold the center part of the outer surface of end wall 6 of the same
container. Accordingly, bushing 107 may be considered as part of cavity
member 174.
Referring to Figs. 12 and 14, cavity member 174 is formed with two
diametrically opposed slots 180 and two circularly curved extensions 182 at
the
inner ends of slots 180 (for convenience, only one slot 180 and one extension
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182 is shown). As seen in Fig. 12, a flat circular groove 184 is formed in
cavity
member 174 adjacent each extension 182. Also the side of each slot 180 facing
front plate 102 is formed with a semi-cylindrical groove 186 that extends to
g roove 184.
Disposed in each of the two diametrically-opposed slots 180 is an insert
block 188. The inner face of each insert block 188 is formed with a
semicircular
slot 190 that complements the adjacent extension 182 of cavity member 174, but
is sized so as to leave a gap therebetween to receive plastic material to form
one
of the ears 12 on the container. Each insert block 188 also has a semi-
cylindrical groove 194 that complements the adjacent groove 186 in cavity
member 174. Each pair of grooves 186 and 194 forms a cylindrical hole in which
is located a core pin 196 (Fig. 12).
Core pin 196 is slidably mounted in a bore 198 in a block 200 that is an
extension of insert block 188 and is affixed to support plate 110. A spring
202
surrounds the shaft of each pin 196 in an enlarged part of bore 198 and acts
against the pin head 204 to urge the pin away from the core 48. The inner end
of each core pin 196 is tapered (beveled) to conform to the tapered openings
18
in ears 12. Core pins 196 are moved toward core 148 by means of two cam bars
206 that are attached to and extend rearwardly from front plate 102. Cam bars
206 occupy diametrically opposed positions relative to the axis of core member
148. Each cam bar 206 is aligned with one of the blocks 200, and each block
200 is slotted fore and aft (vertically as viewed in Figs. 6A, 7A and 12),
with that
slot being sized so that the associated cam bar 206 makes a close sliding fit
therein. The inner end of each cam bar 206 has a slanted cam surface 208 that
is located so that it can engage the head 204 of the adjacent core pin 196
when
the mold assembly is closed (Fig. 6). In this connection it should be noted,
as
shown in Fig. 12) that the outer end surface of each core pin head 204 is
slanted
at substantially the same angle as cam surface 208, so as to facilitate
camming
of core pin 196 by cam bar 206 in the manner hereinafter described. When the
mold assembly is moved to its closed position (Figs. 6A, 6B), blocks 200 move
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with back plate 104 and support plate 110 toward front plate 102, causing core
pin heads 204 to engage cam surfaces 208 of cam bars 206, whereupon the
core pins 196 are cammed inwardly toward core 148. The cam surfaces 208
force core pins 196 inward to a limit position in which their tapered inner
ends
are spaced from curved cavity extensions 182 by an amount equal to the desired
thickness of walls 16 of ears 12.
Referring now to Figs. 7A, 7B and 10A, 10B, it is to be noted that the end
surface 129 of head 120 of poppet 118 forms a mirror image of a major portion
of the inner end surface 178 of cavity member 174, and the inner end surface
of
bushing 107, and that the corresponding annular end surface 149 of core
member 148 is the mirror image of the remainder of surface 178, i.e., the
front
end surface 129 of head 120 of poppet 118 and the surrounding end surface 149
of core member 148 cooperate with inner end surface 178 of cavity member 174
and the inner end surface of bushing 107 to define the container bottom wall
section of the mold cavity in which the container is molded. Also, ring member
146 acts as an auxiliary cavity member since it forms an extension of cavity
member 174 and coacts with core member 148 to determine the shape of the rim
section of the formed container 160. Accordingly when the mold is closed, the
confronting and mutually spaced surfaces of core member 148 and ring member
146, cavity member 174 and insert blocks 188 coact to define the container
side
wall section and the container rim section of the mold cavity in which the
container is molded.
Operation of the above-described mold assembly is straightforward.
Assume that the mold assembly is mounted in an injection molding machine,
with front plate 2 and back plate 4 secured to a fixed platen and a movable
platen respectively of the machine. Assume also that ejector plate 6 is
attached
to a mechanical operator (not shown) that forms part of the same injection
molding machine and is adapted to move the ejector plate toward and away from
front plate 2 at predetermined times during the operating cycle of the
machine.
The sprue hole bushing 107 is connected to a source of plastic (not shown)
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which is to be injected into the closed mold assembly via a suitable injection
pump (also not shown). Assume also that the machine has just completed its
operating cycle, so that (1 ) the mold is in its fully closed position (Figs.
6A, 6B),
with ejector plate 106 engaging or located adjacent to back plate 104, and
core
plate 108 locked to ejector plate 106 by latch bar 124 and spaced back from
support plate 110; and (2) a formed plastic container 160 occupies the mold
cavity defined by core 148, cavity member 174, sprue bushing 107, ring 146,
insert blocks 188 and core pins 196. The machine is programmed so as to
automatically and repeatedly execute an operating cycle which comprises the
following steps starting with the mold in the closed position shown in Figs.
6A
and 6B.
1. The mold is opened by moving back plate 104 and ejector plate
106 together away from front plate 102 (Figs. 7A, 7B). When the mold is
opened, the back plate 104 is moved away from front plate 102 a distance that
exceeds the longitudinal dimension of the cavity of cavity member 174 by an
amount sufficient to permit subsequent removal of the formed container 160
(Figs. 10A, 10B). The rearward movement of back plate 104 away from front
plate 102 causes blocks 188 and 200 to move clear of cam bars 206, freeing
core pins 196 and allowing springs 202 to move those core pins outwardly away
from the curved extensions 182 of cavity member 174. It should be noted that
during the rearward mold-opening movement of back plate 104 and ejector plate
106, the core plate 108 remains locked to ejector plate 106. As the mold is
opened, the formed container 160 remains in place because of its interlocking
engagement with ring member 146 and core member 148. Spring 143 acts to
extend pressure pins 139 as the mold is opened, causing the pins to exert a
force on core plate 108 so as to prevent the latter from moving away from back
plate 104 in the direction of plate 102.
2. Immediately after the mold has been opened, the machine moves
ejector plate 106 (and hence poppet 118) a selected distance away from back
plate 4 (Figs. 8A, 8B). By way of example but not limitation, this movement is
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about 2 inches in the case of molding a one gallon container for paint. During
this movement, core plate 108 is locked to ejector 106 plate and hence it and
core 148 move with the ejector plate. As seen in Figs. 8A, 8B, this initial
movement of ejector plate 106 moves core plate 108 into contact with or
immediately adjacent to support plate 110. This joint movement of poppet 118
and core 148 is sufficient to strip the molded container free of ring member
146.
It also is sufficient to move the rim portion of the formed container beyond
the
insert blocks 188, thereby allowing for lateral expansion of the formed
container
160 as it is freed subsequently from core 148.
In this connection it should be noted that the wall-molding surface 164 of
core member 148 has a larger diameter than its surfaces 166 and 168 which
help mold the inner rim section 22 of the container. Accordingly the rim end
of
the formed container needs to expand outwardly as it is being forced off of
the
core member by relative movement of poppet 118 (see step 3 below). The
molded container 160 has sufficient flexibility and resiliency to permit it to
expand
radially enough to fit over and slide along the core member under the driving
influence of the poppet. In this connection it should be appreciated that this
radial expansion could not occur without the prior limited movement of core
member 148 by ejector plate 106, that limited movement being sufficient to
move
the formed container away from the ring member far enough to prevent the
insert
blocks 188 from restricting expansion of the rim section of the formed
container
as its rim section moves axially from the reduced diameter portion (surfaces
166
and 168) to the increased diameter portion (surface 164) of the core member.
3. Thereafter, as core plate 108 engages support plate 110, cam bar
122 cams pin 132 inward of hole 134, thereby unlocking ejector plate 106 from
core plate 108, and the machine continues to move the ejector plate further
toward front plate 102. Preferably, as shown in Figs. 9a, 9B, the machine
moves
ejector plate 106 into face-to-face contact or near face-to-face contact with
core
plate 108. This action achieves the result of moving the poppet relative to
the
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core plate in a forward direction toward front plate 102, thereby forcing the
formed container 160 off of core member 148.
4. Once the poppet has moved the formed container free of the core
member, the container is removed from the poppet (Figs. 10A, 10B). This may
be done manually, in which case the machine is programmed to stop indefinitely
to allow safe removal of the formed container, after which the machine can be
commanded manually to resume its operating cycle. Preferably, however, the
machine is provided with means (not shown) for automatically removing the
formed container from the machine, with the machine being programmed to
resume operation automatically immediately after removal of the molded
container.
5. Following removal of the formed container, ejector plate 106 is
retracted away from front plate 102 back to the position shown in Figs. 8A,
8B.
At the beginning of this retracting movement, core 148 remains stationary and
latch bar 124 moves relative to cam bar 122 away from front plate 102.
However, after the ejector plate has moved back a limited distance, e.g.,
about 6
inches, projection 130 of latch bar 124 engages the core plate at notch 132.
Substantially simultaneously shoulder 140 moves past detent pin 132,
whereupon spring 138 pushes that pin into slot 128. As a result, core plate
108
is again locked to the ejector plate.
6. Ejector plate 106 completes its rearward movement back to its
original position (Figs. 6A, 6B), carrying core plate 108 with it. As a
result, when
ejector plate 106 again rests against or adjacent to back plate 104, core
plate
108 will be stopped by pillar 114 a limited distance from support plate 110,
as
shown in Figs. 7A, 7B.
7. Thereafter back plate 104 and ejector plate 106 (and also core
plate 108) are moved back toward front plate 102 far enough to cause core
member 148 to mate with cavity member 174 (Figs. 6A, 6B). As this occurs,
cam bars 206 will re-engage core pins 196 and force them inward to molding
position.
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8. The cycle of operation is completed by again injecting molten
plastic material into the formed cavity via sprue bushing 107. It is to be
understood that the mold assembly stays in its closed position (Figs. 6A, 6B)
long enough to allow the injected molten plastic material to cool and
solidify, after
which the mold assembly is opened according to step (1 ) above.
Mold assemblies embodying the present invention may be provided for
molding containers in sizes larger or smaller than the conventional one-gallon
size commonly used by American paint manufacturers. Although the illustrated
mold assembly was designed to mold containers with substantially straight side
walls, it is contemplated that the cavity-defining components may be modified
so
as to provide for injection molding of containers that have a tapered side
wall,
with the containers having their maximum outer diameter at the top ends and
their minimum outer diameter at their bottom ends. Also the mold assembly may
be modified so as to eliminate formation of the strengthening rib 8, and/or to
form
other strengthening contours, recognizing that the need or desire for such
feature may result from one or more factors or functions, e.g., container
size,
overall weight of the contents of the container, and the material of which the
container is made. The mold assembly also may modified to vary the number of
gripping ribs 36 on the rim section of the container. Also the mold assembly
may
be modified to totally eliminate formation of locking ribs 36, in which case
the lid
may be locked to the container rim solely as a result of the rib sections 70
and 80
being compressed together between and gripped by surfaces 32 and 40.
Although it is preferred to make the containers and lids of a high density
polyethylene, the mold assembly of the present invention may be used to
injection mold containers of other plastics materials known to persons
'skilled in
the art, e.g., polypropylene. Colored, clear or translucent plastic may be
used in
molding containers. The mold assembly also can be modified so as to mold the
container with embossed printing on its side wall so as to eliminate the need
for
a subsequent labeling operation. The mold assembly also may be modified to
mold containers having a rim section that is shaped differently from the rim
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section of the container shown in Figs. 1-3. Still other changes will be
obvious to
persons skilled in the art from the foregoing description and the drawings.
The invention offers a number of advantages. Perhaps the most
important advantage is that the invention provides a mold assembly for forming
a
container wherein the rim section extends inwardly of the inner surface of the
container, and accomplishes this without having to use a collapsible core
which
is expensive to make and maintain. Another important advantage is that the
invention makes it possible to manufacture a plastic container for use in
holding
paint or other products in liquid or particulate form that has sufficient
strength to
allow it to be filled, capped, labeled, and stacked or packaged using
conventional
filling, labeling and packaging machinery. Still other advantages provided by
this
invention are that the formed containers have a one-piece construction and, if
desired, free of any seams or crimps.
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